The most common syndromes associated with obstructive lung disease are asthma and chronic obstructive pulmonary disease (COPD). Evidence for a viral etiology of asthmatic exacerbations is well known, but evidence for a role for viruses in COPD exacerbation is just emerging. Viruses may cause chronic infection in both diseases. This paper reviews some studies on the effects of respiratory viruses on asthma and COPD published in 2002 and discusses their relevance to current thinking in pulmonary medicine.